'\" et
.TH POSIX_TYPED_MEM_GET_INFO "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
posix_typed_mem_get_info
\(em query typed memory information
(\fBADVANCED REALTIME\fP)
.SH SYNOPSIS
.LP
.nf
#include <sys/mman.h>
.P
int posix_typed_mem_get_info(int \fIfildes\fP,
    struct posix_typed_mem_info *\fIinfo\fP);
.fi
.SH DESCRIPTION
The
\fIposix_typed_mem_get_info\fR()
function shall return, in the
.IR posix_tmi_length
field of the
.BR posix_typed_mem_info
structure pointed to by
.IR info ,
the maximum length which may be successfully allocated by the typed
memory object designated by
.IR fildes .
This maximum length shall take into account the flag
POSIX_TYPED_MEM_ALLOCATE or POSIX_TYPED_MEM_ALLOCATE_CONTIG specified
when the typed memory object represented by
.IR fildes
was opened. The maximum length is dynamic; therefore, the value
returned is valid only while the current mapping of the corresponding
typed memory pool remains unchanged.
.P
If
.IR fildes
represents a typed memory object opened with neither the
POSIX_TYPED_MEM_ALLOCATE flag nor the POSIX_TYPED_MEM_ALLOCATE_CONTIG
flag specified, the returned value of \fIinfo\fR->\fIposix_tmi_length\fR
is unspecified.
.P
The
\fIposix_typed_mem_get_info\fR()
function may return additional implementation-defined information in
other fields of the
.BR posix_typed_mem_info
structure pointed to by
.IR info .
.P
If the memory object specified by
.IR fildes
is not a typed memory object, then the behavior of this function is
undefined.
.SH "RETURN VALUE"
Upon successful completion, the
\fIposix_typed_mem_get_info\fR()
function shall return zero; otherwise, the corresponding error status
value shall be returned.
.SH ERRORS
The
\fIposix_typed_mem_get_info\fR()
function shall fail if:
.TP
.BR EBADF
The
.IR fildes
argument is not a valid open file descriptor.
.TP
.BR ENODEV
The
.IR fildes
argument is not connected to a memory object supported by this
function.
.P
This function shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
An application that needs to allocate a block of typed memory with
length dependent upon the amount of memory currently available must
either query the typed memory object to obtain the amount available, or
repeatedly invoke
\fImmap\fR()
attempting to guess an appropriate length. While the latter method is
existing practice with
\fImalloc\fR(),
it is awkward and imprecise. The
\fIposix_typed_mem_get_info\fR()
function allows an application to immediately determine available
memory. This is particularly important for typed memory objects that
may in some cases be scarce resources. Note that when a typed memory
pool is a shared resource, some form of mutual-exclusion or
synchronization may be required while typed memory is being queried and
allocated to prevent race conditions.
.P
The existing
\fIfstat\fR()
function is not suitable for this purpose. We realize that
implementations may wish to provide other attributes of typed memory
objects (for example, alignment requirements, page size, and so on).
The
\fIfstat\fR()
function returns a structure which is not extensible and, furthermore,
contains substantial information that is inappropriate for typed memory
objects.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIfstat\fR\^(\|)",
.IR "\fImmap\fR\^(\|)",
.IR "\fIposix_typed_mem_open\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<sys_mman.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
